Abstract : The most important factor among the radio wave propagation path constants with regard to micro-waves whose path lies across the surface of the sea is the value of the effective reflection coefficient rho sub e. In the present survey propagation experiments were carried out with a 9Gc band on real sea surfaces at a distance of 3.52 Km respectively from the transmitter. Three experiments were carried out, two in winter (November, 1959 and February-March, 1961) and one in summer (August, 1959). Measurements of rho sub e by means of the antenna height pattern method, and of the size of the waves at the reflection points were carried out simultaneously. The waves were shown in wave height values, and a hydraulic gauge was employed. As a result of the experiment it became clear that the rho sub e value of the surface of the sea and its short-term variation distribution bear a close relationship to the size of the waves and the motion thereof. Thus, (1) the rho sub e value decreases rather as the size of the waves increases, (2) the variation in rho sub e increases as the waves increase, (3) as a result of the sea waves extremely short fading cycles occur. Appended is some research on determining rho sub e for a rough surface in motion such as the sea, and on the method of measuring rho sub e. (Author)